If you're a regular visitor to Frick Park, you may have seen signs over the last several months indicating that several "Gentle Giants" were scheduled for removal from the park. Over the last several days, these beautiful oak trees have come down, leaving about a two-acre swath of bare ground near the intersection of the Kensington and Hawthorne trails on the northeast edge of the park. The reason? Oak wilt, an aggressive fungus that kills thousands of oak trees each year in the eastern United States.
Oak wilt is a vascular disease that causes leaf wilt, branch dieback, and ultimately death in affected trees. Arborist Stephen Miller of Bartlett Tree Experts, who coordinated the removal with the City of Pittsburgh, likens it to cholesterol clogging a person's veins. The disease is easily spread between trees by insects and by root grafts that develop between trees in the same species group that are growing within 100 feet of each other. Suddenly, one infected tree becomes three infected trees, and the disease spreads outward like wildfire.
It's this rapid rate of infection that made the clearing of this area of the park necessary. Trenches were dug to prevent the infection from traveling through the root system to healthy trees in the area. This week's removal included trees that had already been killed, some that were obviously infected, and some on the border that were potential carriers of the disease. By removing a few on the outer edge, the potential for the disease to continue spreading was greatly reduced. In about a month, arborists will return and inject a fungicide into 44 trees outside the infection area to reduce the risk of future infection.
Infected wood has been put through the wood chipper by the folks at Land Clearing Specialists, who will eventually grind the chips down to an even finer powder. The chips dry out the wood, killing the fungus. The "border" trees that had to be sacrificed to prevent the disease from spreading had healthy wood, which will be put to a higher use as lumber.
"This is absolutely the right thing to do," says Phil Gruszka, the Pittsburgh Parks Conservancy's Director of Parks Maintenance and Management. "It is an unfortunate event in the life of an urban forest, but doing nothing would mean greater devastation." Gruszka, who is a certified arborist, also sees the opportunity to study the effect of such devastation on urban forests. "Learning from catastrophic events is very important in preparing us to respond correctly for future events, and how to effectively manage the aftermath."
A Learning Opportunity
Land clearing of this scale is rare inside the city limits, and especially in a city park. Miller and the staff at Bartlett Tree Experts wanted to use the tree removal as a chance to educate the community about humans' relationship to the life cycle of the forest. So this week, three classes from the Environmental Charter School at Frick Park came to the site to observe some heavy machinery at work and to learn why these trees were lost and what that means for the ecosystem as a whole.
Over the next year, these classes will return to the site to watch its progress. The ground will remain untouched so that the students (as well as Bartlett and the Parks Conservancy) can observe what plants begin to come up on their own now that the area receives full sun and is free of trees. Using hula hoops, the students will search the same area over a period of time to see what plants, insects, and other items of interest appear. Miller is interested in learning what native species, as well as invasive ones, will begin to stake their claim on the land when left to their own devices.
"When the settlers first came here," Miller points out to the students, "they had to fight back the trees in order to make fields to grow their crops. Things want to grow here." No one wants to see two acres of trees succumb to disease, but now we have a very interesting opportunity to study how a forest floor performs when there's suddenly no tree canopy.
"Ideally, native species will take over and there will be no need for further intervention," says Gruszka. And we'll have a front-row seat as the forest begins to invent itself anew.